Indoor Air Quality Studies Research Articles

Maintaining Optimal Indoor Air Quality

In the study of indoor air quality in mixed-use complexes, the focus lies on understanding the intricate balance required to maintain optimal Indoor Air Quality (IAQ). Mixed-use environments present a unique challenge due to the diverse sources of indoor pollutants they encompass. By employing a survey research design that integrates both qualitative and quantitative data analysis, the study aims to shed light on the effectiveness of various strategies in controlling pollutant sources and ensuring well-maintained HVAC systems to improve IAQ. The findings of this research underscore the need to adopt a holistic approach to achieve and sustain optimal levels of IAQ levels within mixed-use complexes. Recommendations such as implementing high-efficiency filtration systems and enhancing ventilation mechanisms emerge as crucial steps towards improving air quality and ultimately enhancing the comfort and well-being of occupants in these multifaceted environments. This comprehensive approach not only addresses the immediate concerns related to IAQ but also contributes to the overall sustainability and liveability of mixed-use complexes, aligning with the growing emphasis on green technologies and practices in modern architectural design.

Assessments and application of low-cost sensors to study indoor air quality in layer facilities

Indoor poultry facilities often experience poor air quality due to intensive farming and restricted ventilation. Monitoring the air quality in these barns is crucial considering the health of both the birds and producers. Advancements in sensor technologies have led to the development of low-cost sensors (LCS) that can continuously monitor air pollutants. Even though most poultry facilities in Canada are indoors due to harsh winter weather conditions, there is a lack of indoor air quality (IAQ) studies. This study aimed to evaluate the field performance of the LCS network in a table egg farm in Canada, where the sensors were designed specifically for operating in dusty poultry facilities continuously. The LCS monitored IQA parameters such as particulate matter (PM), carbon dioxide (CO2), relative humidity, and temperature in real-time. By implementing a correction factor, the sensor data resulted in an agreement range of 80 ± 20% with a reference instrument. The study observed that PM concentration exceeded several thousand μg/m3, with PM10 at 5.5 × 104 ± 2.2 × 104 and PM2.5 at 6.3 × 103 ± 2.3 × 103, which was found to be most affected by the chicken activity and light regime. The IAQ parameters also exhibited a complex intercorrelation with each other, as well as the outdoor temperature and the building ventilation rate. Sensors were able to make observations that were found only with research-grade instruments in previous studies. Overall, the study showcases the potential of the LCS network as an affordable solution for environmental monitoring in poultry facilities.

A comparative study of indoor and outdoor air quality and associated potential health effects in Gurugram, India.

Abstract Deteriorating air quality remains a leading reason for global human illness and death. This study aims to investigate and compare inside and outside ambient air quality in 15 locations of Gurugram, India. Research technique adopted comprised of extracting outdoor air quality parameter values via Air Quality Index reporting stations for the entire year 2022. Parallel to that, indoor air quality parameter values of houses close to those monitoring stations were recorded through low-cost IoT based AirCubic sensors (T1595) as PM2.5, PM10, relative humidity (RH) and carbon monoxide (CO). After statistical evaluation, it was found that there were significant variations in outdoor and indoor air quality with maximum variations seen in colder season. The study revealed that PM levels were generally lower inside homes than outsides, while CO and RH concentrations were higher indoors. However, these levels often exceeded the acceptable thresholds set by both Indian national and global air quality standards, that could potentially result in harmful health effects, as well as increased risk of short and long-term illnesses, and even death. It may be concluded that more research, extensive air quality monitoring, data sharing, citizen awareness, and better technical and policy inputs are required to maintain healthy air quality for a sustainable lifestyle.

Indoor Air Quality: Bibliometric Analysis of the Published Literature Between 2018 and 2023

ABSTRACTThis bibliometric study employs a rigorous approach to scrutinize and visually represent the existing body of literature on indoor air quality (IAQ). Utilizing the Scopus collection database, we conducted an exhaustive exploration of published research literature in the IAQ field. The study involves a thorough visual analysis using Harzing's Publish and Perish and VOSviewer software programs, examining parameters such as citations, publication year, journals, authors, research institutions, countries, and research topics. A total of 1729 pieces of literature related to IAQ research from 2018 to 2023 were retrieved. The dominant formats were articles and conference papers, underscoring their significance in IAQ documentation. Primary subject areas included “Engineering” and “Environmental Science,” highlighting the multidisciplinary nature of IAQ studies. The upward trend in IAQ publications, reaching 330 articles in 2023, emphasizes the growing importance of this field. However, citation impact varied, emphasizing the need to assess research quality alongside quantity. Global distribution identified leading countries, including the United States, China, and the United Kingdom, which were also top contributors in co‐authorship and country‐level analyses. The top journals were “Building and Environment” and “Sustainable Cities and Society,” showcasing varying publication and citation powers. Notable impactful articles in the IAQ domain were led by Agarwal et al. and Van Tran, Park, and Lee. Keyword co‐occurrence analysis identified thematic clusters, with keywords such as “Indoor Air Quality (IAQ),” “Air Quality,” and “Indoor Air Pollution” dominating the literature. Through a comprehensive analysis of published literature, this study provides a visual representation of studies with significant contributions to the IAQ field, offering insights into its development and changes from 2018 to 2023. The findings also guide future IAQ research directions.

Numerical analysis on mechanical ventilation impact on indoor air quality in a basement

Indoor air quality (IAQ) in confined spaces like bank vaults and basements is influenced by complex factors such as building layout and HVAC systems. This study examines how mechanical ventilation impacts IAQ in a bank building's occupied basement vault, addressing significant challenges posed by pollutant exposure in these air-tight environments. This study advances safe IAQ in confined spaces, crucial for occupant health and safety, using CFD (ANSYS Fluent Workbench 16.0) and CONTAM 3.2 software for multi-zone ventilation and air quality analysis. It analysed three indoor pollutants: Radon (Rn), Carbon dioxide (CO2), and Particulate Matter (PM2.5), enhancing the reliability and applicability of the findings. The findings indicated that the simulated indoor pollutants concentrations did not exceed the indoor air quality guideline levels. The CFD simulations predicted average steady-state values of 27.2 Bq/m3 for Radon, 574.80 ppm for CO2, and 69.36 µg/m3 for PM2.5 in the basement. For different outdoor air floor rates, an optimal ventilation rate of 4.7 ACH and a cooling load of 17 kW were determined to maintain Radon concentrations below 15 Bq/m3. This provides a practical and actionable solution for maintaining safe IAQ in confined spaces, which is a significant step forward compared to similar studies. These results align with other experimental research, validating the use of numerical techniques in indoor air quality studies. By optimizing HVAC systems to maintain IAQ and minimize energy consumption, the study supports SDG 7 (Affordable and Clean Energy) by enhancing energy efficiency, SDG 3 (Good Health and Well-being) by reducing exposure to indoor pollutants, and SDG 11 (Sustainable Cities and Communities) by improving air quality management in confined spaces. The findings are particularly relevant for Africa, offering practical solutions, informing policy direction, and supporting the African Union's Agenda 2063 and SDGs 3, 7, and 11.

Spatial mapping of indoor air quality in a light metro system using the geographic information system method

Abstract It is known that one of the greatest problems of developed countries in the twenty-first century is traffic. For this reason, engineers have searched for alternative solutions to the problem of traffic. One such solution is the construction and utilization of rail systems instead of main roads. From an engineering perspective, rail systems can be divided into three groups: metro, light metro, and tram systems. Light metro systems, which are a form of public transportation, are not directly inside the traffic. Their most important advantages include the fact that they do not release combustion products such as CO, and metro and light metro systems may be considered environmentally friendly based solely on their electricity consumption. In this study, measurements of parameters affecting indoor air quality were made inside light metro cars and in and around light metro stations belonging to the light metro system of the Metropolitan Municipality of Antalya, known as the tourism capital of Turkey. In February and March 2021, when the COVID-19 pandemic was first registered in Turkey, particulate matter (PM), temperature, and relative humidity measurements were made for testing indoor and outside air quality. Moreover, as outside air parameters, outside temperature, outside relative humidity, CO, normalized difference vegetation index, and ultraviolet aerosol index data were obtained from the General Directorate of Meteorology of Turkey. The measurement results were analyzed using the inverse distance weighting method in the geographic information system. Based on the results of the analyses, spatial maps were created for indoor and outside air quality parameters in the light metro system. Using these maps, the effects of passenger density and environmental factors both inside the metro cars and at the metro stations on indoor air quality were identified. In addition, the spread of the SARS-CoV-2 virus in the COVID-19 period was analyzed using spatial maps of the PM0.3 and PM0.5 parameters. It is believed that the results of this study will set an example for further indoor air quality studies worldwide, and this study is unique in that it employed a method that is used particularly in survey and geomatics engineering for analyzing indoor air quality in light metro systems.

An empirical study of indoor air quality in badminton stadiums in hot summer and cold winter regions of China during spring and fall seasons

The indoor air quality has a direct impact on human health. In order to obtain the current status of indoor air quality in typical sports buildings in hot summer and cold winter climate zones in China, indoor badminton courts in 10 cities in Hubei Province in this climate zone were selected as research objects for field testing of indoor environmental parameters in spring and autumn, and predict air quality parameters for non-testing times. All the tested stadiums are naturally ventilated in non-event conditions, and the average daily indoor CO2 concentration was 526.78 ppm in spring and 527.63 ppm in autumn, and the average daily PM2.5 concentration was 0.035 mg/m3 in spring and 0.024 mg/m3 in autumn, all of which met the requirements of GB/T 18883-2022, the average concentration of CO2 ≤ 1000 ppm and PM2.5 ≤ 0.05 mg/m3. The indoor CO2 concentration and PM2.5 concentration of the tested badminton halls under natural ventilation gradually increased with the accumulation of exercise time, making the indoor air quality of the badminton halls decrease, which would negatively affect the health of the people exercising in this environment.

Outdoor trends and indoor investigations of volatile organic compounds in two high schools of southern Italy

Volatile organic compounds (VOCs) are a class of ubiquitous substances that are present in outdoor and indoor air. They are emitted by a wide range of sources and can penetrate and accumulate specifically in indoor environments. Concern is growing among the scientific community regarding the potential health impacts of exposure to a high concentration of VOCs in indoor spaces. Due to their still-developing respiratory and immune systems, children may be the most fragile subjects in this regard, and therefore, the study of indoor air quality in schools is of the utmost importance. In this work, the concentrations of total volatile organic compounds (TVOCs) and of 20 specific compounds belonging to this class were determined in a school in Squinzano, a town in the province of Lecce (Apulia region, southern Italy). Sampling was carried out in indoor (classrooms and bathrooms) and outdoor (terrace) areas using passive diffusive samplers for VOCs and photoionization detectors for TVOCs. Average concentrations of both TVOC (303 ± 47 µg m−3) and individual VOCs (< 0.5 µg m−3) were below levels of concern; however, specific indoor sources such as cleaning activities and student occupancy were responsible for peaks in TVOC concentrations above harmless levels for children and school staff. The data were then compared to the ones obtained in a similar study conducted in a school in Galatina, another town of the Apulia region, highlighting the impact of the surrounding outdoor environment on the indoor profile of VOCs.

Experimental Study of Indoor Air Quality in Educational Buildings: A Spanish Case Study

Ensuring good indoor air quality in the spaces within educational centres is essential for the health and academic performance of students. In this sense, studying the evolution of health pollutants and their relationship with the environmental parameters of indoor humidity and temperature presents a challenge for the design of more efficient and comfortable buildings with a lower risk of virus infection. In this work, the relationship between pollution levels and SARS-CoV-2 virus infections in the academic year 2021/22 is shown, comparing the pollution values measured on-site with the value of the official measuring stations of the Community of Madrid. In addition, the impact of ventilation measures implemented during this period is assessed, aiming to establish guidelines for ensuring a safer and healthier school environment. It was found that during winter months, when there is less outdoor ventilation, pollution levels exceeded the recommended limits, according to reference regulations. This highlights the need for interior conditioning strategies in educational spaces. Thus, this multidimensional approach, considering both airborne pollutants and weather conditions, provides a comprehensive perspective on indoor air quality in school buildings in the central area of a metropolitan city, such as the Community of Madrid.

A multi-city study of indoor air quality in green vs non-green low-income housing

ObjectivesThe condition of the home is a strong predictor of exposure to environmental contaminants, with low-income households being particularly vulnerable. Therefore, improving housing standards is a priority. Housing built to “green” standards, with improved building methods and materials, has been suggested to reduce contaminants. However, evidence is limited as to which contaminants are reduced. The Green Housing Study was conducted to address this issue. The study hypothesis was that housing built using green components has lower concentrations of environmental contaminants compared to conventional housing. MethodsA repeated-measures, 12-month cohort study was performed in three U.S. cities. Data were collected in the home at three time points throughout a year. The level of contaminants were estimated using air samples for particulate matter and black carbon, dust samples for aeroallergens and pesticides, and resident or study staff reporting evidence of mold. To investigate source(s) of PM2.5 and black carbon, multivariable models using stepwise variable selection were developed. ResultsIn adjusted generalized estimating equations (GEE) models, black carbon concentration (μg/m3) (β = −0.22, 95% CI = −0.38 to −0.06, p = 0.01), permethrin (OR = 0.28, 95% CI = 0.15–0.49, p < 0.0001), and reported mold (OR = 0.29, 95% CI = 0.13–0.68, p = 0.003) were significantly lower in green homes. Cockroach antigen was also lower in green homes (OR = 0.59, 95% CI = 0.33–1.08, p = 0.09), although not statistically significant. We found that 68% of PM2.5 was explained by dwelling type and smoking and 42% of black carbon was explained by venting while cooking and use of a gas stove. ConclusionsThis study provides quantitative data suggesting benefits of incorporating green building practices on the level of numerous environmental contaminants known to be associated with health. Occupant behavior, particularly smoking, is an important contributor to indoor air pollution.

Is poor air quality in day-care centres’ affecting our children’s health? A study of indoor air quality in childcare facilities located in Perth, Western Australia

Poor indoor air quality (IAQ) can adversely affect children’s health; however, limited studies have quantified indoor air pollutants in day-care centres (DCCs) where infants and young children are increasingly spending more time from a younger age. The aim of this study was to investigate seasonal IAQ in Western Australian childcare facilities at both heavy traffic and low traffic locations. In 22 centres, total volatile organic compounds, formaldehyde, nitrogen dioxide, carbon dioxide, and carbon monoxide, particulate matter (PM) measured in six size fractions (total PM, PM10, PM4, PM2.5, PM1, ultrafine particles), and meteorological parameters (temperature and relative humidity), were continuously sampled over a 24-h period, in the cold season and repeated in the warm season. All contaminants (other than formaldehyde) in the summer and/or winter collections, or averaged over both seasons, were found to be above contemporary air quality standards, guidelines, best practice statements, or other available guidelines developed to protect human health. Furthermore, all contaminants were present at higher concentrations indoors where a DCC was located within 100 m of a heavy traffic roadway. The findings of this study suggest that children who attend these facilities on a regular basis may be chronically exposed to a range of health damaging contaminants during critical stages of their development. The findings support the need for measures to reduce concentrations of air pollutants in DCCs. Preventative actions such as attention to DCC siting, selection of appropriate building materials and furnishings, improvement in ventilation, and usage of ‘green’ cleaning products should be considered to reduce children’s exposures to harmful airborne contaminants.

Long-term analysis of indoor air quality and thermal comfort in a public school

The paper is focused on the investigation of the Indoor Air Quality (IAQ) in two classrooms from a thermal renovated school from Bucharest, related to indoor carbon dioxide (CO2), ozone (O3) concentrations or airborne particles (PM2.5), by using experimental data. The experimental campaign has been conducted over a long period (February-June 2022), allowing the study of indoor air quality under different weather data conditions. The results showed that the use of classroom ventilation is mandatory in order to reach a satisfactory degree of thermal comfort and indoor air quality and even the natural ventilation by windows opening remains a simply and useful tool to lower the indoor pollutant concentrations. However, if the target is to ensure permanent good indoor air quality in these learning spaces, a mechanical ventilation system is more adapted than the natural ventilation, due to the fact it is independent of the weather factors variation (outside temperature and wind velocity and direction).

A Literature Review of Indoor Air Quality and Sick Building Syndrome in Office Building Design Environment

Building indoor spaces requires constant access to fresh air for occupants’ health, well-being, and performance. Clean breathing air can be achieved through the removal of pollutants from within the building’s interior by ensuring a sufficient outdoor air exchange rate. This review set out to create a clear understanding of recent developments in indoor air quality (IAQ) studies and their relationship to sick building syndrome (SBS) impacts on occupants’ health and well-being, as well as the role architectural design plays in promoting a healthy indoor environment. It also provides support information as well as existing state-of-the-art practices in IAQ and SBS in office buildings, with a particular focus on monitoring, assessment, and space configuration. The information available here would provide building professionals, particularly architects, with the potential for incorporating design and the development of guidelines for the control of SBS-related environmental parameters in order to create a healthy and comfortable office indoor environment.

Exploring environmental policy adoption enablers for indoor air quality management in higher educational institutions in South Africa

Purpose: This study seeks to investigate the extent to which the indoor air quality (IAQ) management of higher educational institutions (HEIs) in South Africa could be improved through the appropriate implementation of environmental policy adoption enablers. Multiple challenges have been documented to the improvement of IAQ standards in HEIs. However, an alternative to the management of IAQ is possible through environmental behavioral change.Research Methodology: A philosophical stance of post-positivism influences the adoption of a quantitative research approach for this study. Primary data on the views shared by various academic and administrative staff employed by HEIs across South Africa were collected using a closed-ended questionnaire survey. A literature review uncovered 16 influential environmental policy adoption enablers that could further the objective of the study. A four-phase data analytical approach was adopted to interpret the empirical data through screening and reliability assessment, together with descriptive and inferential statistical evaluations, to ascertain the influence held by the surveyed policy adoption enablers on improving the management of IAQ in HEIs.Results: The inferential statistical evaluation using exploratory factor analysis revealed three crucial environmental policy adoption metrical approaches (stakeholder dialogue, institutional commitment, and policy composition) to the management of IAQ in HEIs.Discussion: From a practical perspective, the administrative council of HEIs could consider the identified policy adoption enablers as a catalyst for pro-environmental behavior and the management of IAQ in all respective institutions. Theoretically, this study contributes to the body of knowledge by providing factors associated with environmental policy adoptions for IAQ management and laying the groundwork for future research in environmental behavior, this has been lacking in previous IAQ studies and current environmental management discourse. As an instrumental enabler, the identified policy adoption approaches could inform any existing or new institutional policy adoption initiative aimed at improving current individuals’ perception of workplace comfort, satisfaction, and performance directly associated with their indoor environmental conditions.

Occupant's health and energy use in an office building: A sensor-enabled life cycle assessment

Indoor air quality (IAQ) has an important impact on human health and productivity. For this reason, its integration into the life cycle assessment (LCA) framework contributes to sustainably manage the operation of a building and improve the living and working conditions in homes and offices. In this study, the damages on human health caused by IAQ are quantified starting from the air pollutants’ concentrations recorded by dedicated sensors placed in an office building located in Luxembourg. Data on concentrations of total volatile organic compounds, particulate matter and radon are combined with estimated occupancy and intake fractions to calculate the total human health impact expressed in Disability Adjusted Life Years (DALYs). The impacts of indoor air quality on human health prove to be relevant, representing one tenth of the score obtained in a conventional LCA on the operational phase of the building. It can be highlighted that radon, a substance usually overlooked in IAQ studies, had the highest impact, contributing to 46% of the impact caused by exposure to indoor pollutants. The heating loads and the influence of different air exchange rates are analyzed starting from a simplified energy model of the building fed with real energy use data. LCA has proven a useful tool to analyze this trade-off in the operation of the building, where it is found that doubling the ventilation rate would reduce the impact of indoor pollutants on human health by 34% while resulting in less than 1% increase in the total energy demand over the studied period.

Numerical Study of Indoor Air Quality in a University Professor’s Office

Indoor air conditioning is currently a topic of much interest, not only to save energy but also due to public health issues such as pandemics. This study focuses on the thermal comfort and air quality of a closed, air-conditioned space located in an extremely hot climate. Due to noise and weather conditions, the door and window of the space are kept closed at all times. The study uses computational fluid dynamics techniques and the finite element method. Average temperatures and CO2 concentrations, as well as effectiveness for temperature and concentration distribution, are calculated for the analysis. Results indicate that supplying air away from hot walls improves air quality and thermal comfort. Furthermore, there is an optimal Reynolds number that depends on the number of people inside the space. Due to the above, it is possible to find an ideal configuration that simultaneously allows for efficient energy use, helps to avoid the adverse effects of CO2 on daily activities such as working or studying, and supports people’s health and comfort.

Indoor air quality monitoring and management in hospitality: an overarching framework

PurposeThis study aims to provide a comprehensive framework for the study of indoor air quality (IAQ) in hospitality premises. The goal is to identify the drivers of air pollution, both at the exogenous and endogenous level, to generate insights for facility managers.Design/methodology/approachThe complexity of hospitality premises requires an integrated approach to properly investigate IAQ. The authors develop an overarching framework encompassing a monitoring method, based on real-time sensors, a technological standard and a set of statistical analyses for the assessment of both IAQ performance and drivers, based on correlation analyses, analysis of variance and multivariate regressions.FindingsThe findings suggest that the main drivers of IAQ differ depending on the area monitored: areas in contact with the outdoors or with high ventilation rates, such as halls, are affected by outdoor air quality more than guestrooms or fitness areas, where human activities are the main sources of contamination.Research limitations/implicationsThe results suggest that the integration of IAQ indicators into control dashboards would support management decisions, both in defining protocols to support resilience of the sector in a postpandemic world and in directing investments on the premises. This would also address guests’ pressing demands for a broader approach to cleanliness and safety and support their satisfaction and intention to return.Originality/valueTo the best of the authors’ knowledge, this is the first study developing a comprehensive framework to systematically address IAQ and its drivers, based on a standard and real-time monitoring. The framework has been applied across the longest period of monitoring for a hospitality premise thus far and over an entire hotel facility.

Indoor air quality study in four Malaysian hospitals for centralized and non-centralized ACMV systems

Indoor air quality study in four Malaysian hospitals for centralized and non-centralized ACMV systems

A process for creating data report-back tools to improve equity in environmental health

BackgroundAlthough there is increasing interest in reporting results of environmental research efforts back to participants, evidence-based tools have not yet been applied to developed materials to ensure their accessibility in terms of literacy, numeracy, and data visualization demand. Additionally, there is not yet guidance as to how to formally assess the created materials to assure a match with the intended audience.MethodsRelying on formative qualitative research with participants of an indoor air quality study in Dorchester, Massachusetts, we identified means of enhancing accessibility of indoor air quality data report-back materials for participants. Participants (n = 20) engaged in semi-structured interviews in which they described challenges they encountered with scientific and medical materials and outlined written and verbal communication techniques that would help facilitate engagement with and accessibility of environmental health report-back materials. We coupled these insights from participants with best practice guidelines for written materials by operationalizing health literacy tools to produce accessible audience-informed data report-back materials.ResultsThe resulting data report-back materials had a 7th -grade reading level, and between a 4th -8th grade level of overall document complexity. The numeracy skills required to engage with the material were of the lowest demand, and we incorporated best practices for risk communication and facilitating understanding and actionability of the materials. Use of a rigorous assessment tool provides evidence of accessibility and appropriateness of the material for the audience.ConclusionsWe outline a process for developing and evaluating environmental health data reports that are tailored to inspire risk-reduction actions, and are demonstrably accessible in terms of their literacy, numeracy, and data visualization demand. Adapting health literacy tools to create and evaluate environmental data report-back materials is a novel and evidence-based means of ensuring their accessibility.

A predictive model of indoor PM2.5 considering occupancy level in a hospital outpatient hall

The hospital outpatient hall is more complex and sensitive than other indoor places because of its high density, flow of patients, and risk of infection. The prediction of indoor pollutants, such as PM2.5, is a critical health risk factor and an important topic in the study of indoor air quality. Numerous black-box models have been built to predict PM2.5, which are prone to overfitting and low precision in long sequence time prediction due to their limited weighting calculation and factors considered In this study, subject-object weighting incorporates a long sequence time-series model that considers occupancy (SO-LSTS) to predict PM2.5 concentrations in a hospital outpatient hall. First, the occupancy level was obtained using image recognition technology. Second, both the subjective (improved AHP) and objective (entropy weight) information were coupled by a distance function and then integrated into the LSTS model. Finally, the model performance was compared to six traditional models and the impact on the output length and hyper-parameter confirmation was assessed. The results demonstrate that the occupancy factor can improve the model performance by 54 %, and the model accuracy is improved by 89 % compared to the traditional Informer method. Our study considers real-time environmental and occupancy levels, which can compensate for the difficulty of interpreting the black-box model and identifying an accurate and resource-efficient proactive control model for hospital environmental management compared to conventional approaches.